The present invention relates video transmission systems, and more specifically to such systems in which the amount of transmitted video information is limited, and in which important video information is automatically selected for transmission.
Many automated security and observation systems include video cameras that view an area of interest. Information from the video camera may be provided real-time via conventional television communication links to a display for monitoring by a human observer, and for storage on tape that may be replayed later. The human observer can identify potential targets (a "target" being any subject that is desirably detected by the system) and manually train the camera for closer observation. In one such system, the railroad car identification system disclosed in U.S. Pat. No. 4,876,597 issued to Roy, et al. Oct. 24, 1989, a fixed video camera is turned on by passage of a train.
In some situations, conventional television communications links for transmitting video information are not adequate. For example, it may be desirable to send video data via a radio transmission system with a bandwidth too narrow to accommodate the desired transmission speeds (e.g., high frequency (HF) radio bandwidth is too narrow for conventional real-time television signals.) One solution to this problem is to transmit less information by eliminating some of the video data. As discussed in U.S. Pat. No. 5,128,776 issued to Scorse, et al. Jul. 7, 1992, an operator may selectively designate important portions of the video data to be transmitted with no or visually lossless compression, and other less significant portions of the data with higher compression. However, human observers are still needed to identify the important portions of the data and the camera field of view.
Where portions of a video image appear consistently and are of predetermined appearance and aspect, such as in a video telephone that displays a human head facing the camera, a processor may locate this predetermined portion of the video image. When the head has been located and a boundary for the video data representing the head has been identified, the processor may reduce the amount of video data being transmitted by reducing the amount of data transmitted for portions outside the boundary relative to portions inside the boundary. (See U.S. Pat. No. 4,951,140 issued to Ueno, et al. Aug. 21, 1990.) However, such a system will only detect targets having the predetermined appearance and aspect.
Movement may also be used to reduce the amount of image data being transmitted. That is, it is known to use moving object detectors to identify movement by comparing sequential video images. Assuming that the moving portions are of interest, the amount of data for portions of the video image that are stationary may be reduced. (See, for example, U.S. Pat. No. 4,692,806 issued to Anderson, et al. Sep. 8, 1987.) In such systems, the moving object detector "tracks" the moving object (in other words, the least compressed portion of image data moves with the moving object). As is apparent, however, image data for an important portion of the image that may not be moving, or that is not moving enough to trigger the moving object detector, may be compressed; for example, important image data for a target may be inadvertently compressed when the target is headed directly for the camera.
Accordingly, it is an object of the present invention to provide a novel image transmission system and method of transmitting images that obviates the problems of the prior art.
It is a further object of the present invention to provide a novel method and video image compression system that automatically detects a target in an area of interest and transmits a digital video image of the target in which nontarget information in the area of interest is automatically compressed before transmission.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.